Photoinhibition of microbial nitrification in potable water

ABSTRACT

A system for the photo-inhibition of microbial nitrification of potable water may include overhead, floating or submerged lamps (fluorescent, incandescent, LED, etc. . . . ) with spectral emission between 315-430 nm, headspace and submerged light meters for measuring the intensity above and below the water surface, a water mixing device to manage full water column dose, and a controller for operating associated lamp and mixer operations. The applied irradiance may typically be equal to or exceed 0.01 W/m 2 .

BACKGROUND OF THE INVENTION

The present invention generally relates to apparatus and methods forcontrolling microbial nitrification and more specifically, to apparatusand methods for providing a dose of ultraviolet-A (UVA)/Visible light incovered drinking water storage facilities to control nitrification.

It is well established in the scientific literature that the enzymesused by nitrifying microbes to first oxidize ammonia to nitrite and thennitrite to nitrate are inhibited by UVA and visible light. Potable wateris often stored in large water storage tanks. Nitrifying microbes mayproduce nitrites and nitrates through the oxidation of ammonia producedby the degradation of chloramine disinfectant.

In covered drinking water storage, nitrification contributes to the lossof disinfectant residual, stimulates the growth of other nuisancemicrobes and produces nitrite and nitrate, both of which are regulateddrinking water contaminants. Nitrate is the cause of methemoglobinemia(blue-baby syndrome) in infants.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a system for thephoto-inhibition of microbial nitrification of potable water comprises atank for holding water; and at least one lamp irradiating light into thewater.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdrawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of incident irradiance over a spectrum between 250 and700 nm for a variety of lamps;

FIG. 2 a graph showing the incident irradiance of an exemplaryblue-blocking blacklight lamp (BLB) through various lenses;

FIG. 3 shows a lighting design according to an embodiment of the presentinvention;

FIG. 4 is a schematic drawing of a water storage tank having a microbialnitrification photo-inhibition system according to an exemplaryembodiment of the present invention;

FIG. 5 is a schematic drawing of a water storage tank having a microbialnitrification photo-inhibition system according to an alternateexemplary embodiment of the present invention;

FIG. 6 is an engineering drawing of an exemplary storage tank used inthe various studies described below;

FIG. 7 is a bar graph showing UVA intensity at various points,horizontally, at 4 feet above ground level (AGL) in air in the storagetank of FIG. 6;

FIG. 8 is a bar graph showing UVA intensity at various points,vertically, at 28″ from the wall of the storage tank of FIG. 6.

FIG. 9 is a bar graph showing UVA intensity at various points,vertically, at 28″ from the wall of the storage tank of FIG. 6, over athree day period;

FIG. 10 is a graph describing results of a bottle test with and withoutthe microbial nitrification photo-inhibition system of the presentinvention;

FIG. 11 a is a chart describing the distribution of UVA intensity withdepth at high water, including estimates of the time to half-inhibitionfor each flux; and

FIG. 11 b is a chart describing the distribution of UVA intensity withdepth at low water, including estimates of the time to half-inhibitionfor each flux.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplatedmodes of carrying out exemplary embodiments of the invention. Thedescription is not to be taken in a limiting sense, but is made merelyfor the purpose of illustrating the general principles of the invention,since the scope of the invention is best defined by the appended claims.

Various inventive features are described below that can each be usedindependently of one another or in combination with other features.

Broadly, embodiments of the present invention generally provide aninhibiting dose of UVA/Visible light in covered drinking water storagefacilities to prevent nitrification. Embodiments of the currentinvention use UVA/Visible radiation to control bacterial nitrificationin an industrial setting.

As used herein, an “inhibiting dose” of UVA/Visible light may beradiation at a suitable wavelength and intensity over a specific periodof time, typically 24 hours or less, to inhibit enzymes used innitrifying microbes. For example, an inhibiting dose may be radiationhaving a wavelength between 315 and 430 nanometers (nm) and an incidentirradiance of at least 0.01 watts per square meter (W/m²) over a periodof 24 hours, typically at least 0.01 W/m².

As used herein, the term “photo-inhibition”, with respect to microbialnitrification, refers to not only the prevention of microbialnitrification in water, but also to the treatment of microbialnitrification once such a process has started. Similarly, “reducing”microbial nitrification of water refers not only to lessening the rateand/or degree of microbial nitrification, but also to the elimination ofmicrobial nitrification of water.

Referring to FIG. 1, there is shown a graph of incident irradiance overa spectrum between 250 and 700 nm for a variety of lamps. After severaltests and exploration of a variety of lamps, a blue-blocking blacklightlamp was chosen as the lamp to use in the below described experiments.While this specific lamp was chosen for further study, the inventionshould not be limited to any particular lamp, provided that the lamp mayprovide an adequate dose to achieve the desired result of inhibitingmicrobial nitrification. For example, fluorescent, incandescent or LEDlamps may be useful in various embodiments of the present invention.

Referring to FIG. 2, there is shown a graph of the irradiance of anexemplary blue-blocking blacklight lamp (BLB) through various lenses. Inthis graph, the emission spectrum of the BLB lamp is shown by the linewith the circles. This line should be read against the Y-axis on theleft. The other three lines show the percent transmission of the BLBemission spectrum through various lenses—a stock lens (triangle-markedline), a UVA transmitting lens (diamond-marked line), and two stackedUVA transmitting lenses (square-marked line). As can be seen, the UVAtransmitting lenses provided a greater transmittance throughout theentire measured spectrum (335-400 nm).

Referring now to FIG. 3, there is shown a lighting design useful in awater storage tank, according to an embodiment of the present invention.The lighting design uses a number of light banks 30, each containing atleast one lamp, such as at least one F40T12BLB median bipin fluorescentlamp (not shown). The exemplary lighting design of FIG. 3 may be basedon comparative scans of warm white lamps with suitable design software.The lighting design of FIG. 3 should be taken as an exemplary lightingdesign and should not be considered as limiting the choice of lightingdesign useful in the present invention.

Referring to FIG. 4, there is shown a schematic drawing of a waterstorage tank 40 having a microbial nitrification photo-inhibition systemaccording to the present invention. The system may include a pluralityof lamps 42, such as the BLB lamps as described above. The lamps may becontrolled by a timer 44. The output of the lamps 42 may be measured byat least one light meter 46. Typically, a number of light meters 46 maybe disposed at various locations above ground level (AGL). For example,as shown in FIG. 4, three light meters 46 may be disposed along one sideof the water storage tank 40. While the lamps 42 are shown above thewater level, the lamps 42 may be located at various locations inside thewater tank 40, such as above the water level, submerged in the waterwithin the tank 40, or floating on top of the water in the tank 40.

In one exemplary embodiment of the present invention, as shown in FIG.5, a water storage tank 50 may be similar to the water storage 40described above, with the addition of a dimmer 52 for controlling theintensity of the output of the lamps. The water storage tank 50 may alsoinclude a mixing device 54 for mixing water stored in the tank 50. Themixing device 54 may be controlled by a timer 56. Control of the variouscomponents, such as the lamps, timers, dimmers, mixing devices and thelike may be performed on-site or remotely via any known controltechnique. For example, a Supervisory Control and Data Acquisition(SCADA) system may be used to remotely control the system of the presentinvention.

Referring to FIG. 6, there is shown an engineering drawing of anexemplary storage tank used in the various studies described below. FIG.7 shows the UVA intensity at various points horizontally at 4 feet aboveground level (AGL) in air in the storage tank of FIG. 6. FIG. 8 showsthe UVA intensity at various points, vertically, at 28″ from the wall ofthe storage tank of FIG. 6. FIG. 9 shows showing UVA intensity atvarious points, vertically, at 28″ from the wall of the storage tank ofFIG. 6, over a three day period.

Referring now to FIG. 10, there is shown a graph describing results of abottle test with and without the microbial nitrificationphoto-inhibition system of the present invention. In this study, three5-liter pyrex bottles, containing 3 liters of water in each, weresuspended from two water storage tanks (six 5-liter pyrex bottles intotal). The bottles were placed 3.5 feet above ground level in eachtank. Nitrification had begun in the water sample prior to filling thepyrex bottles. One tank was kept in the dark and one tank was providedwith UVA/Visible light according to an embodiment of the presentinvention. As can be seen from the graph of FIG. 10, after 3 days, thetanks in the dark were of considerably poorer quality compared to thoseunder light.

Referring to FIG. 11 a, there is shown a chart describing thedistribution of UVA intensity with depth at high water, includingestimates of the time to half-inhibition for each flux. FIG. 11 b showsa chart describing the distribution of UVA intensity with depth at lowwater, including estimates of the time to half-inhibition for each flux.

It should be understood, of course, that the foregoing relates toexemplary embodiments of the invention and that modifications may bemade without departing from the spirit and scope of the invention as setforth in the following claims.

1. A system for the photo-inhibition of microbial nitrification ofpotable water, the system comprising: a tank for holding water; and atleast one lamp illuminating the water.
 2. A method for reducingmicrobial nitrification of potable water, the method comprising:contacting the water with radiation having a wavelength between 315 and430 nm; and providing a sufficient intensity to contact all of the waterat an incident irradiance of at least 0.01 W/m².